Install packages

if ! which netcat >/dev/null || nc -N 2>&1 | grep -q 'invalid option'  2>&1
then
    if which apt-get >/dev/null 2>&1; then
        apt-get update
        apt-get install -y zstd netcat-openbsd pv #  mariadb-backup
        ln -s /bin/nc.openbsd /usr/local/bin/netcat
    elif which yum >/dev/null 2>&1; then
        yum install -y netcat pv zstd \
        https://archive.mariadb.org/mariadb-10.3.17/yum/rhel/7.4/x86_64/rpms/MariaDB-backup-10.3.16-1.el7.centos.x86_64.rpm
    else
        echo 'ERROR!'
    fi
fi

Start listener on slave, first. Progress shown is (compressed) network traffic incoming from source/master.

NETCAT_PORT=3306
IMPORT_DIR=/srv/mysql-import
MYSQL_DIR="$(mysql -Bse "SELECT @@datadir" 2>/dev/null )" || MYSQL_DIR=/srv/mysql

which firewall-cmd 2> /dev/null && firewall-cmd --add-port=$NETCAT_PORT/tcp
systemctl stop mariadb
mkdir -pv "$IMPORT_DIR" $MYSQL_DIR
[ -z "${MYSQL_DIR}" ] || rm -rvf "$MYSQL_DIR"/*
[ -z "${IMPORT_DIR}" ] || rm -rvf "$IMPORT_DIR"/*
netcat -l $NETCAT_PORT \
  | pv \
  | zstd -dcf \
  | mbstream --directory="$IMPORT_DIR" -x --parallel=$(nproc) \
&& time mariabackup --prepare --target-dir="$IMPORT_DIR" \
&& mariabackup --move-back --target-dir="$IMPORT_DIR" \
&& mv "$IMPORT_DIR/xtrabackup_binlog_info" "$MYSQL_DIR" \
&& rm -rf "$IMPORT_DIR" \
&& install -o mysql -g mysql -d "$MYSQL_DIR"/{,tmp,binlog} /var/{log,lib}/mysql \
&& chown -R mysql:mysql "$MYSQL_DIR" /var/{log,lib}/mysql \
&& systemctl start mariadb 

Progress shown is uncompressed db size. –parallel=$(nproc) does not work out well on systems with a lot of cpu cores - too many connections. Parameter –kill-long-queries-timeout prevents long READ LOCK (RO-mode of whole databases) on db01, killing queries that have been running when establishing the READ LOCK.

• Ankündigung: 5 Sekunden Read Lock, siehe oben
• in tmux, open mytop -d mysql session before starting transfer so in case of „too many connections“ there is still an open root session
• start transfer: 

  CU=lmx
  SLAVE=db02.$CU.xres.rz1.xtrav.de
  NETCAT_PORT=3306
  MYSQL_DIR=$(mysql -Bse 'SELECT @@datadir')

  db_size=$(LANG=C du -csm $MYSQL_DIR/*/*.{ibd,frm,MYD,MYI} $MYSQL_DIR/ibdata* | awk '/total$/{print $1}')
  mariabackup --backup --stream=xbstream --parallel=2 --kill-long-queries-timeout=5 2> mariabackup.log \
    | pv -s ${db_size}m\
    | zstd -1 \
    | netcat -N $SLAVE $NETCAT_PORT \
  && tail mariabackup.log

Replication user name is derived from slave host name

CU=lmx
MASTER=db01.$CU.xres.rz1.xtrav.de
SLAVE=db02.$CU.xres.rz1.xtrav.de

replication_id=${SLAVE%%\.*} \
&& replication_user=replication_$replication_id \
&& replication_pass="$(tr -dc '[:alnum:]' < /dev/urandom | head -c 32 && echo)" \
&& mysql -Bse "
  DELETE FROM mysql.user WHERE user=\"$replication_user\";
  GRANT REPLICATION SLAVE ON *.* TO $replication_user@\"%\"
  IDENTIFIED BY \"$replication_pass\";
  FLUSH PRIVILEGES;
" 
echo "RUN ON SLAVE:"
echo
cat << SLAVE_END
MYSQL_DIR="\$(mysql -Bse "SELECT @@datadir" 2>/dev/null )"
read LOG_FILE LOG_POS GTID < "\$MYSQL_DIR/xtrabackup_binlog_info" 
if [ -z "\$LOG_POS" ] || [ -z "\$MYSQL_DIR" ]
then
    echo "ERROR - could not read from '\$MYSQL_DIR/xtrabackup_binlog_info'"
else
    mysql -e "
        STOP SLAVE;
        CHANGE MASTER TO
            MASTER_HOST='$MASTER',
            MASTER_PORT=3306,
            MASTER_USER='$replication_user',
            MASTER_PASSWORD='$replication_pass',
            MASTER_LOG_FILE='\$LOG_FILE',
            MASTER_LOG_POS=\$LOG_POS;
        START SLAVE;
    "
fi
sleep 2
mysql -Bse "SHOW SLAVE STATUS\G"
SLAVE_END

Paste RUN ON SLAVE: output above and check replication state:

mysql -Bse "SHOW SLAVE STATUS\G"